System and methods for controlling the amplitude modulation of noise generated by wind turbines

ABSTRACT

In one aspect, a method for controlling the amplitude modulation of the noise generated by wind turbines is disclosed. The method may include determining a rotor position of a first wind turbine, determining a rotor position of a second wind turbine, determining if the first and second wind turbines are operating in-phase and, in the event that the first and second wind turbines are operating in-phase, adjusting an operating condition of at least one of the first wind turbine and the second wind turbine so that the first and second wind turbines operate out-of-phase.

FIELD OF THE INVENTION

The present subject matter relates generally to wind turbines and, moreparticularly, to a system and methods for controlling the amplitudemodulation of noise generated by wind turbines.

BACKGROUND OF THE INVENTION

Wind power is considered one of the cleanest, most environmentallyfriendly energy sources presently available, and wind turbines havegained increased attention in this regard. A modern wind turbinetypically includes a tower, generator, gearbox, nacelle, and one or morerotor blades. The rotor blades capture kinetic energy of wind usingknown foil principles. The rotor blades transmit the kinetic energy inthe form of rotational energy so as to turn a shaft coupling the rotorblades to a gearbox, or if a gearbox is not used, directly to thegenerator. The generator then converts the mechanical energy toelectrical energy that may be deployed to a utility grid.

During operation of a wind turbine, the rotation of the rotor bladesthrough air generates aerodynamic noise. Due to the amplitude modulation(i.e., the peak-to-peak variation) of the aerodynamic noise, a“swooshing” or periodic pulsing sound is typically heard in the nearfield of the wind turbine (i.e., the area directly around the windturbine). Such sounds are typically seen as a nuisance and, thus,regulations are typically put in place establishing maximum decibel (dB)levels for wind turbines operating around residential communities andother populated areas. As a result, wind turbines are typically designedto operate below these maximum dB levels. However, current research nowsuggests that the peak-to-peak amplitude of the modulated noisegenerated by wind turbines may be higher at locations in the far field((i.e., locations a certain distance (e.g., 1-4 kilometers) away fromthe wind turbines) than in the near field due to propagation effectsand/or constructive interference. As such, there is a risk that windturbines operating below the maximum dB levels in the near field mayactually be exceeding these levels in the far field.

Various methods have been proposed for reducing the noise emissions ofwind turbines. For example, it has been proposed to reduce aerodynamicnoise by de-rating all of the wind turbines within a wind turbine farmin order to keep turbine speeds low during time intervals (e.g., duringnighttime or other times at which reduced noise is desired). However,such de-rating of the wind turbines significantly reduces the powerproduction of the farm. Another proposed method is to actively pitch theblades of a wind turbine as the blades pass through a particular rangeof azimuth positions (e.g., pitching the blades as they pass from theone o'clock to the four o'clock position). However, similar to de-ratingthe wind turbines, such continuous feathering of the blades results in asignificant reduction in overall power production.

Accordingly, a system and method for controlling the amplitudemodulation of noise generated by a wind turbine that does notsignificantly reduce power production would be welcomed in thetechnology.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In one aspect, the present subject matter discloses a method forcontrolling the amplitude modulation of noise generated by windturbines. The method may generally include determining a rotor positionof a first wind turbine, determining a rotor position of a second windturbine, determining if the first and second wind turbines are operatingin-phase and, in the event that the first and second wind turbines areoperating in-phase, adjusting an operating condition of at least one ofthe first wind turbine and the second wind turbine so that the first andsecond wind turbines operate out-of-phase.

In another aspect, the present subject matter discloses a method forcontrolling the amplitude modulation of noise generated by a pluralityof wind turbines of a wind turbine farm. The method may generallyinclude determining a rotor position of each wind turbine of theplurality of wind turbines, determining if any of the wind turbines areoperating in-phase and, in the event that any of the wind turbines areoperating in-phase, adjusting an operating condition of at least one ofthe wind turbines so that the plurality of wind turbines operatesout-of-phase.

In a further aspect, the present subject matter discloses a system forcontrolling the amplitude modulation of noise generated by windturbines. The system may generally include a first wind turbine having afirst rotor position and a second wind turbine having a second rotorposition. The system may also include a controller configured todetermine if the first and second wind turbines are operating in-phaseby comparing the first rotor position to the second rotor position.Additionally, the controller may be configured to adjust an operatingcondition of at least one of the first wind turbine and the second windturbine when it is determined that the first and second wind turbinesare operating in-phase.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 illustrates a perspective view of one embodiment of several windturbines within a wind turbine farm;

FIG. 2 illustrates a simplified, internal view of one embodiment of anacelle of one of the wind turbines shown in FIG. 1;

FIG. 3 illustrates a schematic view of one embodiment of components thatmay be included within the turbine controllers and/or the farmcontroller shown in FIG. 1;

FIG. 4 illustrates a flow diagram of one embodiment of a method forcontrolling the amplitude modulation of noise generated by windturbines;

FIG. 5 illustrates a graphical view of one embodiment of sound wavesgenerated by wind turbines operating in-phase and sound waves generatedby wind turbines operating out-of-phase;

FIG. 6 illustrates a simplified view of a wind turbine farm surroundedby a plurality of receptor locations;

FIG. 7 illustrates a flow diagram of another embodiment of a method forcontrolling the amplitude modulation of noise generated by windturbines;

FIG. 8 illustrates a graphical view of one embodiment of a resultantsound wave that may be produced by interfering and/or augmenting aturbine sound wave with an additive sound wave; and,

FIG. 9 illustrates a perspective view of one of the wind turbines shownin FIG. 1, particularly illustrating a sound meter and speakers locatedrelative to the wind turbine.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

In general, the present subject matter is directed to a system andmethods for controlling the amplitude modulation of noise generated bywind turbines. For example, in several embodiments, two or more windturbines may be controlled so as to prevent such wind turbines fromoperating in-phase relative to one another. As such, the sound wavesgenerated by the wind turbine may be prevented from constructivelyinterfering and producing a resultant sound wave having a peak-to-peakamplitude greater than the peak-to-peak amplitude of any of theindividual sound waves. In other embodiments, additive sound waves maybe generated that interfere with and/or augment the sound wavesgenerated by the wind turbines. Thus, the resultant sound waves may havea peak-to-peak amplitude that is significantly less than thepeak-to-peak amplitude of the sound waves generated by the windturbines.

Referring now to the drawings, FIG. 1 illustrates a perspective view ofone embodiment of several wind turbines 12 located within a wind turbinefarm 10. As shown, each wind turbine 12 includes a tower 14 extendingfrom a support surface 16, a nacelle 18 mounted on the tower 14, and arotor 20 coupled to the nacelle 18. The rotor 20 includes a rotatablehub 22 and at least one rotor blade 24 coupled to and extendingoutwardly from the hub 22. For example, in the illustrated embodiment,the rotor 20 includes three rotor blades 24. However, in an alternativeembodiment, the rotor 20 may include more or less than three rotorblades 24. Each rotor blade 24 may be spaced about the hub 22 tofacilitate rotating the rotor 20 to enable kinetic energy to betransferred from the wind into usable mechanical energy, andsubsequently, electrical energy. For instance, the hub 22 of each windturbine 10 may be rotatably coupled to an electric generator 26 (FIG. 2)positioned within the nacelle 18 to permit electrical energy to beproduced. It should be appreciated that, although only three windturbines 12 are shown in FIG. 1, the wind turbine farm 10 may generallyinclude any suitable number of wind turbines 12.

Additionally, each wind turbine 12 may include a turbine control systemor turbine controller 28 centralized within the nacelle 18. In general,the turbine controller 28 may comprise a computer or other suitableprocessing unit. Thus, in several embodiments, the turbine controller 28may include suitable computer-readable instructions that, whenimplemented, configure the controller 28 to perform various differentfunctions, such as receiving, transmitting and/or executing wind turbinecontrol signals. As such, the turbine controller 28 may generally beconfigured to control the various operating modes (e.g., start-up orshut-down sequences) and/or components of the wind turbine 12. Forexample, the controller 28 may be configured to control the blade pitchor pitch angle of each of the rotor blades 24 (i.e., an angle thatdetermines a perspective of the rotor blades 24 with respect to thedirection of the wind) to control the power output generated by the windturbine 12 by adjusting an angular position of at least one rotor blade24 relative to the wind. For instance, the turbine controller 28 maycontrol the pitch angle of the rotor blades 24, either individually orsimultaneously, by transmitting suitable control signals to a pitchdrive or pitch adjustment mechanism 30 (FIG. 2) of the wind turbine 12.Further, as the direction of the wind changes, the turbine controller 28may be configured to control a yaw direction of the nacelle 18 toposition the rotor blades 24 with respect to the direction of the wind,thereby controlling the load and power output generated by the windturbine 12. For example, the turbine controller 28 may be configured totransmit control signals to a yaw drive mechanism 32 (FIG. 2) of thewind turbine 10 such that the nacelle 18 may be rotated on top of thetower 14.

Moreover, as shown in FIG. 1, the turbine controller 28 of each windturbine 12 may be communicatively coupled to a farm controller 34. Forinstance, in one embodiment, each turbine controller 28 may becommunicatively coupled to the farm controller 34 through a wiredconnection, such as by connecting the controllers 28, 34 through asuitable communicative link (e.g., a suitable cable). Alternatively,each turbine controller 28 may be communicatively coupled to the farmcontroller 34 through a wireless connection, such as by using anysuitable wireless communications protocol known in the art.

Similar to each turbine controller 28, the farm controller 34 maygenerally comprise a computer or other suitable processing unit. Thus,in several embodiments, the farm controller 34 may include suitablecomputer-readable instructions that, when implemented, configure thecontroller 34 to perform various different functions, such as issuingand/or transmitting wind turbine control signals to each turbinecontroller 28. As such, the farm controller 34 may generally beconfigured to control any or all of the turbine controllers 28 in thewind turbine farm 10 in order to change or alter the operating mode ofany number of the wind turbines 12. Specifically, the farm controller 34may be configured to command a single wind turbine 12, particular groupsof wind turbines 12 or all of the wind turbines 12 in the wind turbinefarm 10 to enter into a particular operating mode and/or to perform aparticular action in order to adapt the wind turbine(s) 12 to changingoperating conditions and/or, as will be described below, to facilitate areduction in the amplitude modulation of the noise generated by the windturbine(s) 12.

Referring now to FIG. 2, a simplified, internal view of one embodimentof a nacelle 18 of one of the wind turbines 12 shown in FIG. 1 isillustrated. As shown, a generator 26 may be disposed within the nacelle18. In general, the generator 26 may be coupled to the rotor 20 of thewind turbine 12 for producing electrical power from the rotationalenergy generated by the rotor 20. For example, as shown in theillustrated embodiment, the rotor 20 may include a rotor shaft 36coupled to the hub 22 for rotation therewith. The rotor shaft 36 may, inturn, be rotatably coupled to a generator shaft 38 of the generator 26through a gearbox 40. As is generally understood, the rotor shaft 36 mayprovide a low speed, high torque input to the gearbox 40 in response torotation of the rotor blades 24 (FIG. 1) and the hub 22. The gearbox 40may then be configured to convert the low speed, high torque input to ahigh speed, low torque output to drive the generator shaft 38 and, thus,the generator 26. However, in other embodiments, it should beappreciated that the generator shaft 38 may be rotatably coupleddirectly to the rotor shaft 36. Alternatively, the generator 26 may bedirectly rotatably coupled to rotor shaft 36 (often referred to as a“direct-drive wind turbine”).

Additionally, as indicated above, the turbine controller 28 may also belocated within the nacelle 18. As is generally understood, the turbinecontroller 28 may be communicatively coupled to any number of thecomponents of the wind turbine 12 in order to control the operation ofsuch components. For example, the turbine controller 28 may becommunicatively coupled to the yaw drive mechanism 32 of the windturbine 12 for controlling and/or altering the yaw direction of thenacelle 18 relative to the direction of the wind. Similarly, the turbinecontroller 28 may be communicatively coupled to each pitch adjustmentmechanism 30 of the wind turbine 12 (one of which is shown) forcontrolling and/or altering the pitch angle of the rotor blades 24relative to the direction of the wind. For instance, the turbinecontroller 28 may be configured to transmit a control signal to thepitch adjustment mechanism 30 such that one or more actuators (notshown) of the pitch adjustment mechanism 30 may be utilized to rotatethe blades 24 relative to the hub 22.

Moreover, in several embodiments, the wind turbine 12 may also includeone or more sensors 42 or other suitable devices for detecting and/ormeasuring the azimuth or rotor position of the wind turbine 12. As isgenerally understood, the rotor position of a wind turbine 12 may bedetected and/or measured by determining the angle of rotation of therotor 20 relative to a predetermined rotor position (e.g., thevertically upwards or twelve o'clock position).

It should be readily appreciated that the sensor(s) 42 may generallycomprise any suitable sensor(s) and/or measurement device(s) known inthe art for detecting and/or measuring the rotor position of a windturbine 12. For instance, in one embodiment, the sensor(s) 42 maycomprise one or more rotary or shaft encoders coupled to the rotor shaft36 and/or the generator shaft 38 so that the angular position of suchshaft(s) 36, 38 may be detected/measured and transmitted to the turbinecontroller 28 for subsequent processing/analysis in order to determinethe rotor position of the wind turbine 12. In another embodiment, thesensor(s) 42 may comprise one or more proximity and/or position sensorsconfigured to transmit a signal to the turbine controller 28 each timethe rotor shaft 36, the generator shaft 38 and/or one of the blades 24passes a particular angular position (e.g., the twelve o'clockposition). The turbine controller 28 may then determined the rotorposition of the wind turbine 12 at any given time based on the speed ofthe rotor 20 and/or the generator 26.

In further embodiments, it should be appreciated that the wind turbine12 may also include various other sensors for detecting and/or measuringone or more other operating parameters and/or operating conditions ofthe wind turbine 12. For example, the wind turbine 12 may includesensors for detecting and/or measuring the pitch angle of each rotorblade 24, the speed of the rotor 20 and/or the rotor shaft 34, the speedof the generator 26 and/or the generator shaft 38, the torque on therotor shaft 34, the torque on the generator shaft 36 and/or any otheroperational parameters/conditions of the wind turbine 12.

Referring now to FIG. 3, there is illustrated a block diagram of oneembodiment of suitable components that may be included within theturbine controller 28 and/or the farm controller 34 in accordance withaspects of the present subject matter. As shown, the turbine controller28 and/or the farm controller 34 may include one or more processor(s) 44and associated memory device(s) 46 configured to perform a variety ofcomputer-implemented functions (e.g., performing the methods, steps,calculations and the like disclosed herein). As used herein, the term“processor” refers not only to integrated circuits referred to in theart as being included in a computer, but also refers to a controller, amicrocontroller, a microcomputer, a programmable logic controller (PLC),an application specific integrated circuit, and other programmablecircuits. Additionally, the memory device(s) 46 may generally comprisememory element(s) including, but are not limited to, computer readablemedium (e.g., random access memory (RAM)), computer readablenon-volatile medium (e.g., a flash memory), a floppy disk, a compactdisc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digitalversatile disc (DVD) and/or other suitable memory elements. Such memorydevice(s) 46 may generally be configured to store suitablecomputer-readable instructions that, when implemented by theprocessor(s) 44, configure the turbine controller 28 and/or the farmcontroller 34 to perform various functions including, but not limitedto, determining the rotor positions of one or more wind turbines 12,comparing the rotor positions of differing wind turbines 12 to oneanother, adjusting the operating conditions of one or more of the windturbines 12 and/or determining the sound characteristics of the noisegenerated by one or more wind turbines 12.

Additionally, the turbine controller 28 and/or farm controller 34 mayalso include a communications module 48 to facilitate communicationsbetween the controller(s) 28, 34 and the various components of the windturbine 10 and/or to facilitate communications between each controller28, 34. For instance, the communications module 48 may include a sensorinterface (e.g., one or more analog-to-digital converters) to permit thesignals transmitted by the sensor(s) 42 to be converted into signalsthat can be understood and processed by the processors 44.

Referring now to FIG. 4, there is illustrated one embodiment of a method100 for controlling the amplitude modulation of noise generated by windturbines 12. As shown, the method 100 generally includes determining arotor position of a first wind turbine 102, determining a rotor positionof a second wind turbine 104, determining if the first and second windturbines are operating in-phase 106 and, in the event that the first andsecond wind turbines are operating in-phase, adjusting an operatingcondition of at least one of the first wind turbine and the second windturbine so that the first and second wind turbines operate out-of-phase108.

In general, the method 100 shown in FIG. 4 may be utilized to reduce theamplitude modulation of the noise generated by wind turbines 12 bypreventing such wind turbines 12 from operating in-phase relative to oneanother. Specifically, by monitoring the rotor positions of two or morewind turbines 12 and adjusting the operating conditions of one or moreof such wind turbines 12 when the wind turbines 12 are operatingin-phase, the sound waves generated by the wind turbines 12 may beprevented from constructively interfering and producing a resultantsound wave having a peak-to-peak amplitude greater than the peak-to-peakamplitude of any of the individual sound waves. As such, the amplitudemodulation of the sound waves propagating away from the wind turbines 12and into the far field may be reduced, thereby reducing the magnitude ofthe “swooshing” or periodic pulsing sound that may be heard in the farfield.

As shown in the illustrated embodiment, in 102 and 104, the rotorpositions of both a first wind turbine 12 and a second wind turbine 12may be determined. As indicated above, the rotor position of each windturbine 12 may be actively monitored in real time using the sensor(s)42, turbine controller 28 and/or farm controller 34 described withreference to FIGS. 1-3. For instance, the sensor(s) 42 disposed withinthe first and second wind turbines 12 may be configured to transmitrotor position measurement signals to each turbine controller 28 and/orthe farm controller 34. The signals may then be subsequentlyprocessed/analyzed by the turbine controllers 28 and/or the farmcontroller 34 to determine the rotor position of each wind turbine 12.

Additionally, in 106, the rotor positions of the first and second windturbines 12 may be compared to one another to determine if the windturbines 12 are operating in-phase. In general, a wind turbine 12 may beconsidered to be operating in-phase with another wind turbine 12 whenthe wind turbines 12 are rotating at the same or substantially the samerotor speed and the absolute value of the difference between their rotorpositions is less than a predetermined in-phase tolerance. For instance,in several embodiments, two wind turbines 12 may be considered to beoperating in-phase when the absolute value of the difference betweentheir rotor positions is equal to less than about 20 degrees, such asless than about 10 degrees or less than about 5 degrees or less thanabout 2 degrees or less than about 1 degree. However, it should bereadily appreciated by those of ordinary skill in the art that thepredetermined in-phase tolerance for determining whether wind turbines12 are operating in-phase may generally vary depending on numerousfactors including, but not limited to, the particular configuration ofthe wind turbines 12, operating conditions of the wind turbines 12and/or the sound characteristics (e.g., sound pressure level, modulationfrequency and peak-to-peak amplitude) of the sound waves generated bythe wind turbines 12.

Referring still to FIG. 4, if it is determined that the first and secondwind turbines 12 are operating in-phase, in 108, an operating conditionof the first wind turbine 12 and/or the second wind turbine 12 may beadjusted to bring the wind turbines 12 out-of-phase. For instance, inseveral embodiments, the rotor speed of the first wind turbine 12 and/orthe second wind turbine 12 may be temporarily adjusted, such as bytemporarily increasing or decreasing the rotor speed) so that the rotorposition of the first wind turbine 12 is offset relative to the secondwind turbine 12. However, in other embodiments, any other suitableoperating condition(s) of the wind turbines 12 may be adjusted thatpermits the rotor positions of the wind turbines 12 to be offsetrelative to one another.

It should be readily appreciated by those of ordinary skill in the artthat the rotor speed of a wind turbine 12 may be adjusted using anysuitable means and/or method known in the art. Thus, in severalembodiments, the rotor speed may be adjusted by adjusting the pitchangle of one or more of the rotor blades 24 of the wind turbine 12. Asdescribed above, the pitch angle of the rotor blades 24 may becontrolled by transmitting a suitable control signal to the pitchadjustment mechanism 30 of the wind turbine 12. In other embodiments,the rotor speed may be adjusted by modifying the resistance or torque onthe generator 26, such as by transmitting a suitable control signal tothe generator 26 in order to modulate the magnetic flux produced withinthe generator 26. Alternatively, a braking mechanism (not shown) orother suitable device may be installed within the wind turbine 12 foradjusting the rotor speed of the rotor 20.

It should also be appreciated that, although the method elements 102,104, 106, 108 shown in FIG. 4 generally relate to controlling theamplitude modulation of the noise generated by two wind turbines 12, thedisclosed method 100 may generally be utilized to control the amplitudemodulation of the noise generated by any suitable number of windturbines 12. Thus, in several embodiments, the disclosed method 100 maybe utilized to control the amplitude modulation of the noise generatedby a predetermined group of wind turbines 12 forming part of a windturbine farm 10 (FIG. 1). For example, by analyzing the sound wavesgenerated by each wind turbine 12 within a wind turbine farm 10, it maybe determined that a particular group of wind turbines 12 is generatingsound waves that have an increased amplitude modulation at a particularreceptor location within the far field. As such, the disclosed method100 may be utilized to monitor the rotor positions of that particulargroup of wind turbines 12 in order to control the wind turbines 12 in amanner that prevents them from operating in-phase relative to oneanother.

Referring now to FIG. 5, there is illustrated a comparison of the soundwaves 110, 112 generated by a group of three different wind turbines(i.e., a first wind turbine 114, a second wind turbine 116 and a thirdwind turbine 118) before and after application of the disclosed method100. In particular, the sound waves 110 generated while the windturbines 114, 116, 118 are operating in-phase is illustrated on the leftside of FIG. 5 and the sound waves 112 generated after the rotorpositions of such wind turbines 114, 116, 118 have been offset relativeto one another is illustrated on the right side of FIG. 5.

As shown, the sound waves 110, 112 generated by the wind turbines 114,116, 118 each have the same modulation frequency 120 and peak-to-peakamplitude 122. Thus, when the rotors 20 (FIGS. 1 and 2) of the windturbines 114, 116, 118 are aligned in a time synchronous manner so thatthe wind turbines 114, 116, 118 are operating in-phase, thecorresponding sound waves 110 generated by the wind turbines 114, 116,118 are also in-phase. As such, the peaks 124 and troughs 126 of eachsound wave 110 are generally aligned with one another. Accordingly, inthe event that the sound waves 110 traverse the same space and combine(e.g., at a particular receptor location within the far field), theresultant sound wave generated due to constructive interference may havea peak-to-peak amplitude equal to the sum of the individual peak-to-peakamplitudes 122 of the sound waves 110.

To prevent such constructive interference, an operating condition of atleast two of the wind turbines 114, 116, 118 may be adjusted so that therotor position of each wind turbine 114, 116, 118 is offset from therotor positions of the other wind turbines 114, 116, 118. For instance,as shown on the right side of FIG. 5, an operating condition of thesecond wind turbine 116 may be adjusted (e.g., by temporarily adjustingthe rotor speed of the second wind turbine 116 relative to the rotorspeed of the first wind turbine 114) such that the rotor position of thesecond wind turbine 116 is offset from the rotor position of the firstwind turbine 114 by a first offset angle 128. Similarly, an operatingcondition of the third wind turbine 118 may be adjusted (e.g., bytemporarily adjusting the rotor speed of the third wind turbine 118relative to the rotor speeds of the first and second wind turbines 114,116) such that the rotor position of the third wind turbine 118 isoffset from both the rotor position of the first wind turbine 114 andthe rotor position of the second wind turbine 116. Specifically, asshown, the rotor position of the third wind turbine 118 may be offsetfrom the rotor position of the second wind turbine 116 by a secondoffset angle 130 and, thus, may be offset from the rotor position of thefirst wind turbine 114 by the sum of the first and second offset angles128, 130. By offsetting the rotor positions, a phase difference may becreated between the sound waves 112 generated by each wind turbine 114,116, 118. For instance, as shown in the illustrated embodiment, a 90degree phase difference may exist between each of the sound waves 112.Accordingly, in the event that the sound waves 112 traverse the samespace and combine (e.g., at a particular receptor location within thefar field), the resultant sound wave generated due to interferencebetween the sound waves 112 may have a peak-to-peak amplitude that issignificantly less than the peak-to-peak amplitude of the sound wavethat would otherwise be created when the wind turbines 114, 116, 118 areoperating in-phase.

Additionally, in several embodiments of the present subject matter, thedisclosed method 100 may take into account the affect of the amplitudemodulation of the noise generated by wind turbines 12 at a plurality ofdifferent receptor locations within the far field. For example, FIG. 6illustrates a simplified view of wind turbines 12 within a wind turbinefarm 10 surrounded by a plurality of receptor locations 50. Eachreceptor location 50 may generally correspond to a location within thefar field at which the amplitude modulation of the noise generated bythe wind turbines 12 is regulated and/or is desired to be maintainedbelow a certain threshold. For example, each receptor location 50 maycorrespond to one or more dwellings or other populated areas.

In general, the receptor locations 50 may be located at varyingdistances from the wind turbine farm 10, resulting in varying distancesbetween each receptor location 50 and the various wind turbines 12contained within the wind turbine farm 10. As such, due to the varyingpropagation distances defined between each wind turbine 12 and eachreceptor location 50 (as well as the varying landscapes and atmosphericeffects that may be present between the wind turbines 12 and eachreceptor location 50), the sound waves generated by the wind turbines 12may constructively interfere with another at one receptor location 50and not another. Accordingly, the method 100 disclosed herein may bedesigned to control the wind turbines 12 based on their affect onspecific receptor locations 50 within the far field.

For example, in one embodiment, after it is determined whether any ofthe wind turbines 12 within the wind farm 10 are operating in-phase(e.g., by comparing the rotor positions of the wind turbines 12 to oneanother), an optimization algorithm may be applied to determine how tobring the wind turbines 12 out-of-phase in a way that minimizes theconstructive interference of the sound waves generated by the windturbines 12 at any and/or all of the receptor locations 50.Specifically, the optimization algorithm may include the steps ofidentifying which of the wind turbines 12 within the wind farm 10 affectthe noise heard at each receptor location 50 and then controlling suchwind turbines 12 to ensure that they operate out-of-phase for theaffected receptor locations 50.

In one embodiment, the group of wind turbines 12 affecting the noiseheard at a specific receptor location 50 may be identifiedexperimentally or mathematically, such as by measuring the noise heardat each receptor location 50 when particular wind turbines 10 are inoperation or by calculating which turbines may affect each receptorlocation using the propagation distances defined between each windturbine 12 and the particular receptor location being analyzed.Alternatively, as shown in FIG. 6, a predetermined radius 52 may bedefined around each receptor location 50 within which it is believedthere is a substantial likelihood that the sound waves generated by thewind turbines 12 falling within such radius 52 may constructivelyinterfere with another at the corresponding receptor location 50. Assuch, it may be assumed that the group of wind turbines 12 containedwithin the radius 52 defined for a particular receptor location 50affect the noise heard at such receptor location 50.

Upon determining the group of wind turbines 12 that affect the noiseheard at each receptor location 50, such wind turbines 12 may then bebrought out-of-phase relative to another to reduce the likelihood of thesound waves generated by the wind turbines 12 from constructivelyinterfering at the affected receptor location(s) 50. For example, asdescribed above, an operating condition of one or more of the windturbines 12 (e.g., rotor speed) may be adjusted to bring the windturbines 12 out-of-phase.

It should be appreciated that one or more of the wind turbines 12 withinthe wind turbine farm 10 may affect the noise heard at various differentreceptor locations. For instance, as shown in FIG. 6, the radii definedfor the receptor locations may overlap one another. Accordingly, thewind turbine(s) 12 affecting two or more receptor locations may becontrolled to ensure that they do not operate in-phase with any of theother wind turbines 12 affecting any of such receptor locations.

Referring now to FIG. 7, there is illustrated another embodiment amethod 200 for controlling the amplitude modulation of noise generatedby wind turbines 12. As shown, the method 200 generally includesdetermining a sound characteristic of a turbine sound wave generated bya wind turbine 202 and generating an additive sound wave based on thesound characteristic such that a resultant sound wave is produced havinga peak-to-peak amplitude that is smaller than a peak-to-peak amplitudeof the turbine sound wave 204.

In general, the method 200 shown in FIG. 7 may be utilized to reduce theamplitude modulation of the noise generated by wind turbines 12 bycombining the wind turbine noise with an additive noise. In particular,by determining one or more sound characteristics of the sound wavesgenerated by a wind turbine 12 and generating additive sound waves basedon the sound characteristic(s), a resultant sound wave may be produceddue to interference between the sound waves that has a peak-to-peakamplitude smaller than the peak-to-peak amplitude of the turbine soundwaves. As such, the amplitude modulation of the sound waves propagatinginto the far field may be reduced.

For example, FIG. 8 illustrates a graphical view of one embodiment of aresultant sound wave (indicated by line 210) that may be produced byinterfering and/or augmenting the sound wave generated by a wind turbine12 (indicated by line 212) with an additive sound wave (indicated byline 214). As shown, the turbine sound waves 212 may have particularsound characteristics, such as an average sound pressure level (e.g.,approximately 50.5 dBA in the illustrated embodiment), modulationfrequency 216 and peak-to-peak amplitude 218. Thus, by determining thesound characteristics of the turbine sound waves 212, it may be possibleto introduce additive sound waves 214 that interfere with and/or augmentthe turbine sound waves 212 in order to reduce the overall peak-to-peakamplitude 220 of the resulting noise. For instance, as shown in theillustrated embodiment, additive sound waves 214 may be generated thatinterfere with and/or augment the trough 222 of the turbine sound wave212 without significantly affecting the peak 224 of the turbine soundwave 212. In other words, additive sound waves 214 may be generated suchthat a phase difference exists between the additive sound waves 214 andthe turbine sound waves 212. For example, in several embodiments, thephase difference between the additive sound waves 214 and the turbinesound waves 212 may be equal to about 180 degrees. As such, byappropriately selecting the sound pressure level and/or the peak-to-peakamplitude 226 of the additive sound waves 214 to be generated (e.g., bygenerating additive sound waves 214 having a sound pressure level lessthan that of the average sound pressure level of the turbines soundwaves 212), the peaks 228 of the additive sound waves 214 may be alignedwith and overlap the troughs 222 of the turbine sound waves 212, therebycreating resultant sound waves 210 having a peak-to-peak amplitude 220significantly less than the peak-to-peak amplitude 218 of the turbinesound waves 212. Accordingly, even through an overall increase in noisemay result from the addition of the additive noise, the amplitudemodulation responsible for creating the objectionable “swooshing” orperiodic pulsing sound may be significantly reduced.

It should be appreciated that the sound characteristics of the turbinesound waves 212 may be determined using any suitable means and/or methodknown in the art. For instance, in several embodiments, one or moresound meters 230, such as one or more noise dosimeters, microphones,sound level meters and/or any other suitable sound measurement devices,may be positioned at a location(s) relative to the wind turbine 12 suchthat the sound pressure level, modulation frequency 216 and/orpeak-to-peak amplitude 218 of the turbine sound waves 212 may beaccurately measured and/or determined. Specifically, as shown in FIG. 9,in one embodiment, the sound meter(s) 230 may be embedded within and/ormounted to a component of the wind turbine tower 10 (e.g., the windturbine tower 14). However, in alternative embodiments, the soundmeter(s) 230 may be disposed at any other suitable location relative tothe wind turbine 12 (e.g., a location separate from the wind turbine 12)that allows for the accurate measurement and/or determination of thesound characteristics of the turbine sound waves 212.

Additionally, the sound meter(s) 230 may be communicatively coupled tothe turbine controller 28 and/or the farm controller 34 (e.g., via awired or wireless connection) such that the sound measurement signalsgenerated by the sound meter(s) 230 may be transmitted to the turbinecontroller 28 and/or farm controller 34 for subsequentprocessing/analysis. For instance, the turbine controller 28 and/or thefarm controller 34 may be provided with suitable computer-readableinstructions that, when implemented, configure the controller(s) 28, 34to process and/or interpret the measurement signals in order todetermine the sound characteristics of the turbine sound waves 212.

It should also be appreciated that the additive sound waves 214described above may be generated using any suitable sound generatingdevice known in the art. For example, in several embodiments, one ormore speakers 232 may be mounted to and/or embedded within a portion ofthe wind turbine 12 to permit the additive sound waves 214 to begenerated. Thus, as shown in FIG. 9, in one embodiment, the speaker(s)232 may be mounted to and/or embedded within the nacelle 18 of the windturbine 12. Alternatively, the speaker(s) 232 may be located at anyother suitable location relative to the wind turbine 12, such as on thesupport surface 16 of the wind turbine 12. In addition, the speaker(s)232 may be communicatively coupled the turbine controller 28 and/or thefarm controller 34 (e.g., via a wired or wireless connection). As such,upon determination of the sound characteristics of the turbine soundwaves 212, the turbine controller 28 and/or the farm controller 34 maytransmit suitable signals to the speaker(s) 232 for generating theadditive sound waves 214 necessary to produce resultant sound waves 210having reduced peak-to-peak amplitudes.

In alternative embodiments, the sound generating device may compriseanother aerodynamic noise source. For example, in one embodiment, thesound generating device may comprise a fan or a jet. In anotherembodiment, the nacelle 18 or an electronic cooling system (not shown)of the wind turbine 12 may be modified so that such components generatethe necessary additive sound waves 214.

Additionally, it should be appreciated that the method 200 shown in FIG.7 may be utilized to control the amplitude modulation of the noisegenerated by any number of wind turbines 12. For example, in severalembodiments, each wind turbine 12 within a wind turbine farm 10 (FIG. 1)may include one or more sound meters 230 and speakers 232 for measuringthe sound waves 212 generated by the wind turbine 12 and for generatingadditive sound waves 214 based on the turbine sound waves 214.Alternatively, one or more sound meters 230 may be utilized to measurethe sound characteristics of the sound waves 214 generated by each windturbine within a group of wind turbines 12 and one or more speakers 232may be utilized to generate additive sound waves 212 based on the soundcharacteristics of the sound waves 214. For instance, when two or morewind turbines 12 are operating in-phase, a single speaker 232 or set ofspeakers 232 may be utilized to produce additive sound waves 214 capableof reducing the amplitude modulation of the noise generated by each ofthe wind turbines 12. As such, a resultant sound wave 210 may beproduced that has a peak-to-peak amplitude 220 that is smaller than apeak-to-peak amplitude 218 of each turbine sound wave 212 generated bythe wind turbines 12.

Moreover, it should be readily appreciated that the methods disclosedherein 100, 200 need not be utilized in isolation. For example, acombination of both methods 100, 200 may be utilized to control theamplitude modulation of the noise generated by one or more wind turbines12. Specifically, in one embodiment, when it is desired to control theamplitude modulation of the noise generated by a plurality of windturbines 12 affecting one or more receptor locations 50 within the farfield, the amplitude modulation may be controlled by generating anadditive sound wave for some of the wind turbines 12 and by controllingthe other wind turbines 12 to ensure that they operate out-of-phase.Further, one of ordinary skill in the art should appreciate that thedisclosed methods 100, 200 provide for amplitude modulation control withlittle or no decrease in the power output of a wind turbine 10.

Further, it should be appreciated that the present subject matter isalso directed to a system for controlling the amplitude modulation ofnoise generated by one or more wind turbines. For example, in severalembodiments, the system of the present subject matter may include afirst wind turbine 12 (FIG. 1) having a first rotor position and asecond wind turbine 12 (FIG. 1) having a second rotor position.Additionally, the system may include a controller 28, 34 (FIG. 1)configured to determine if the first and second wind turbines 12 areoperating in-phase by comparing the first rotor position to the secondrotor position. For instance, as described above, each turbinecontroller 28 and/or the farm controller 34 may be communicativelycoupled to one or more sensor(s) 42 (FIG. 2) configured to both measurethe rotor position of a wind turbine 12 and transmit signals relating tosuch rotor position measurements to the controller(s) 28, 34 forsubsequent processing/analysis. Thus, in one embodiment, a firstsensor(s) 42 may be disposed in the first wind turbine 12 for measuringthe first rotor position and a second sensor(s) 42 may be disposed inthe second wind turbine for measuring the second rotor position, withthe controller(s) 28, 34 being communicatively coupled to the first andsecond sensors 42 (e.g., via a wired or wireless connection). Based onthe rotor position measurements received from the first and secondsensors 42, the controller(s) 28, 34 may then determine if the first andsecond wind turbines are operating in-phase, such as by comparing theabsolute value of the difference between the first and second rotorpositions to a predetermined in-phase tolerance. Additionally, thecontroller(s) 28, 34 of the disclosed system may also be configured toadjust an operating condition of the first wind turbine 12 and/or thesecond wind turbine 12 if it is determined that the first and secondwind turbines 12 are operating in-phase. For instance, as describedabove, the controller(s) 28, 34 may adjust the rotor speed of one orboth of the wind turbines 12 to bring the wind turbines 12 out-of-phaserelative to one another.

Of course, one of ordinary skill in the art should appreciate thatsystem described above need not be limited to a first wind turbine 12and a second wind turbine 12, but may generally include a plurality ofwind turbines 12 having a plurality of rotor positions. In such anembodiment, the controller(s) 28, 34 may be configured to both determineif any of the wind turbines 12 are operating in-phase and adjust anoperating parameter of one or more of the wind turbines 12 to ensurethat the wind turbines 12 operate out-of-phase.

In other embodiments, the system of the present subject matter mayinclude a sound meter 230 (FIG. 9) configured to measure a soundcharacteristic of a turbine sound wave 212 (FIG. 8) generated by a windturbine 12, a sound generating device (e.g., one or more speakers 232(FIG. 9) configured to generate an additive sound wave 214 (FIG. 8) anda controller(s) 28, 34 (FIG. 1) communicatively coupled to the soundmeter 230 and the sound generating device. The controller(s) 28, 34 maygenerally be configured to receive sound characteristic measurementsfrom the sound meter 230 and, based on such measurements, control theadditive sound wave 214 generated by sound generating device so that aresultant sound wave 210 (FIG. 8) is produced that has a peak-to-peakamplitude 220 (FIG. 8) that is smaller than a peak-to-peak amplitude 218(FIG. 8) of the turbine sound wave 212.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A method for controlling the amplitude modulation of noise generated by wind turbines, the method comprising: determining a rotor position of a first wind turbine; determining a rotor position of a second wind turbine; determining if the first and second wind turbines are operating in-phase; and in the event that the first and second wind turbines are operating in-phase, adjusting an operating condition of at least one of the first wind turbine and the second wind turbine so that the first and second wind turbines operate out-of-phase.
 2. The method of claim 1, wherein determining if the first and second wind turbines are operating in-phase comprises determining if the difference between the rotor position of the first wind turbine and the rotor position of the second wind turbine is less than a predetermined in-phase tolerance.
 3. The method of claim 2, wherein the predetermined in-phase tolerance is equal to less than about 10 degrees.
 4. The method of claim 2, wherein the predetermined in-phase tolerance is equal to less than about 2 degrees.
 5. The method of claim 1, wherein adjusting an operating condition of at least one of the first wind turbine and the second wind turbine so that the first and second wind turbines operate out-of-phase comprises adjusting a rotor speed of at least one of the first wind turbine and the second wind turbine.
 6. The method of claim 5, wherein adjusting a rotor speed of at least one of the first wind turbine and the second wind turbine comprises adjusting a pitch angle of a rotor blade of at least one of the first wind turbine and the second wind turbine.
 7. The method of claim 5, wherein adjusting a rotor speed of at least one of the first wind turbine and the second wind turbine comprises adjusting a torque on a generator of at least one of the first wind turbine and the second wind turbine.
 8. The method of claim 1, wherein adjusting an operating condition of at least one of the first wind turbine and the second wind turbine so that the first and second wind turbines operate out-of-phase comprises adjusting an operating condition of at least one of the first wind turbine and the second wind turbine so that the rotor position of the first wind turbine is out-of-phase from the rotor position of the second wind turbine by an offset angle.
 9. The method of claim 1, wherein determining a rotor position of a first wind turbine comprises receiving a signal from a sensor disposed within the first wind turbine related to the rotor position of the first wind turbine.
 10. The method of claim 1, wherein determining a rotor position of a second wind turbine comprises receiving a signal from a sensor disposed within the second wind turbine related to the rotor position of the second wind turbine.
 11. The method of claim 1, wherein the first and second wind turbines form part of a plurality of wind turbines disposed within a wind turbine farm and wherein a plurality of receptor locations are disposed around the wind turbine farm, further comprising: determining a rotor position of each wind turbine in the plurality of wind turbines; comparing the rotor position of each wind turbine to the rotor positions of other wind turbines within the plurality of wind turbines to determine if any of the wind turbines are operating in-phase; identifying a group of wind turbines of the plurality of wind turbines that affect noise heard at a particular receptor location of the plurality of receptor locations; in the event that any of the group of wind turbines are operating in-phase, adjusting an operating condition of at least one of the wind turbines of the group of wind turbines so that the group of wind turbines operates out-of-phase.
 12. The method of claim 11, wherein identifying a group of wind turbines of the plurality of wind turbines that affect noise heard at a particular receptor location of the plurality of receptor locations comprises defining a radius around the particular receptor location within which the group of wind turbines is located.
 13. A method for controlling the amplitude modulation of noise generated by a plurality of wind turbines of a wind turbine farm, the method comprising: determining a rotor position of each wind turbine of the plurality of wind turbines; determining if any of the wind turbines are operating in-phase; and, in the event that any of the wind turbines are operating in-phase, adjusting an operating condition of at least one of the wind turbines so that the plurality of wind turbines operates out-of-phase.
 14. The method of claim 13, wherein determining if any of the wind turbines are operating in-phase comprises determining if the difference between the rotor positions of any two wind turbines of the plurality of wind turbines is less than a predetermined in-phase tolerance.
 15. The method of claim 13, wherein adjusting an operating condition of at least one of the wind turbines so that the plurality of wind turbines operates out-of-phase comprises adjusting a rotor speed of at least one of the wind turbines.
 16. The method of claim 13, wherein determining a rotor position of each wind turbine of the plurality of wind turbines comprises receiving a signal from a sensor disposed within each turbine related to the rotor position of each wind turbine.
 17. A system for controlling the amplitude modulation of noise generated by wind turbines, the system comprising: a first wind turbine having a first rotor position; a second wind turbine having a second rotor position; and a controller configured to determine if the first and second wind turbines are operating in-phase by comparing the first rotor position to the second rotor position, the controller being further configured to adjust an operating condition of at least one of the first wind turbine and the second wind turbine when it is determined that the first and second wind turbines are operating in-phase.
 18. The system of claim 17, further comprising a first sensor disposed within the first wind turbine and configured to measure the first rotor position and a second sensor disposed within the second wind turbine and configured to measure the second rotor position, the controller being configured to receive signals from the first and second sensors corresponding to rotor position measurements of the first and second wind turbines.
 19. The system of claim 18, wherein the first and second sensors each comprise at least one of a shaft encoder, a position sensor and a proximity sensor.
 20. The system of claim 17, wherein the controller comprises a farm controller configured to control a plurality of wind turbines of a wind turbine farm. 